Dry Spring Speeds Oroville Repairs

After a record-setting rainy season, California’s dry, hot spring has helped expedite repairs to Oroville Dam’s damaged concrete spillway, but even as work moves forward, some in the state are raising concerns over transparency.

This week, crews on the spillway repair job, overseen by prime contractor Kiewit Infrastructure West, switched to 10-hour shifts starting at 5 a.m. and 8 p.m. in order to avoid the heat of the day, according to the California Department of Water Resources; high temperatures in Oroville have been at or above 105 degrees every day since Sunday (June 18).

Kelly M. Grow / California Department of Water Resources

Demolition of the main spillway's lower chute is nearly complete, and crews will begin to pour a new foundation in July, according to plans.

Last week, state officials said the Kiewit crews were “ahead of schedule” by a matter of days, owing in part to the dry weather the site has seen this spring.

Heavy rains during this year’s rainy season led to a crisis situation in February, when damage to the concrete spillway was uncovered, and dam officials briefly switched the dam’s overflow to a never-used auxiliary spillway. The unpaved emergency spillway eroded quickly, leading to fears a concrete weir could give way, which would have resulted in uncontrolled releases of water into the valley downstream.

Demolition and Concrete Production

On June 17, the contractor began operations at a roller-compacted concrete plant built on the site; the DWR says a total of 800,000 cubic yards of RCC will be used in the reconstruction of the main spillway and the construction of a concrete slab on the auxiliary spillway.

Crews are also establishing a structural concrete plant on the site, where 146,000 cubic yards of concrete will be mixed for use on the spillways. According to the DWR, the structural concrete will require the installation of 8.5 million pounds of reinforcing steel.

Dale Kolke / California Department of Water Resources

On June 17, contractor Kiewit Infrastructure West began operations at a roller-compacted concrete plant built on the site.

During this year’s phase of construction, the lower chute area of the main spillway is being completely demolished; a 1,000-foot section of the upper chute will be patched and waterproofed but left intact this year and replaced next year. Chute demolition is nearly complete, the DWR says, and crews will begin to pour the foundation for the new lower chute in July, according to plans. Crews used excavators and controlled blasts to demolish the lower chute.

Transparency Questions

As the repairs continue, some in the area are expressing concerns about the state’s transparency in relation to dam emergencies.

And an environmental advocacy group filed a suit on June 6 in an effort to force the DWR to hand over records pertaining to asbestos at the Oroville site. In March, the agency revealed that asbestos had been found in rock formations in a limited area at the site, and that some asbestos was detected in the air during debris removal.

The agency said it was monitoring the air for asbestos levels, and crews used wetting and wet-drilling techniques to limit airborne exposure.